ABSTRACT
ABSTRACT Five tropical maize lines were tested and compared with the susceptible control line B73 for resistance to Maize stripe virus (MStV) and Maize mosaic virus (MMV), both propagatively transmitted by the planthopper Peregrinus maidis (Homoptera: Delphacidae). Resistance to each virus was evaluated separately by artificial inoculations with planthoppers viruliferous for either one virus or the other. Disease incidence and symptom severity progression were quantified in relation to time and the cumulative number of planthoppers. Line Hi40 was found to be susceptible to MStV and highly resistant to MMV. Generally, no MMV symptoms developed on Hi40, even under intense inoculation pressure by a large number of viruliferous planthoppers. Line Rev81 showed a partial but strong resistance to MStV, which mainly reduced disease incidence. Nevertheless, this resistance to MStV was the highest ever reported and held up, even when challenged by large numbers of planthoppers. The percentage of infected plants in line Rev81 never exceeded 30 to 40% in our experiments. Moderate levels of resistance to MStV, and to a lesser extent MMV, were found in lines 37-2, A211, and Mp705. However, resistance in these lines was completely overcome using a large number of insects transmitting either of the two viruses. These results suggest that different types of resistance to MMV and MStV are available in maize lines from Caribbean and Mascarene germ plasm. The expression of virus-specific resistance identified in Hi40 and Rev81 lines was not affected by intense inoculation pressure. In contrast, the moderate resistance in 37-2, A211, and Mp705 was partially effective against both viruses but not at high inoculation pressure. These different types of resistance, when present in the same genotype, could provide protection against both viruses.
ABSTRACT
Diaphania hyalinata (L.), the melonworm, causes economic damage in cucurbit species in the Caribbean region. To control larvae feeding on leaves, frequent pesticide applications are needed, but this favors outbreaks of other pests. We looked for plant resistance to D. hyalinata in Cucumis melo L. and two wild Cucumis, C. metuliferus Meyer and C. pustulatus Naudin. Fifteen genotypes were observed using a 1-81 damage scale during 8 wk in two field trials in Guadeloupe, French West Indies. Among the C. melo genotypes, we observed different levels of damage (scores of 32-74 at the maximum damage date) ranging from partially resistant to susceptible genotypes. Both wild species scored <20 at the maximum damage date, and were more resistant in the field tests than the tested genotypes of C. melo. Five C melo genotypes and one C. pustulatus genotype were tested using a detached leaf test. Under controlled conditions, newly hatched larvae were fed with leaves from plants that were 5-9 wk old. Duration and mortality of immature stages were highly correlated. Strong antibiosis (long development and high mortality) was expressed by PI 140471 and Concombre Chien (two C. melo genotypes). For both genotypes, mortality was at least 87.9 versus 34% for Védrantais, a susceptible genotype. Because antibiosis and field resistance were not correlated, we hypothesize that some genotypes expressed antixenosis in the field trials. In addition, possibilities of breeding for C. melo resistance to D. hyalinata is discussed.
Subject(s)
Cucumis melo , Moths , Pest Control, Biological/methods , Animals , Cucumis melo/genetics , Plant LeavesABSTRACT
Plant regeneration from 2-month-old callus cultures derived from immature leaves of 7-day-old aseptic seedlings and mature embryos of the African wild rice Oryza longistaminata was achieved at 20% and 100% frequency, respectively. The morphogenic potential of the embryo-derived calluses dropped from 100% at the third subculture to 12.5 % at the 12th subculture. Five-month-old morphogenic calluses were used to establish a fast-growing suspension culture which, when plated onto semisolid medium, still retained its ability to regenerate plantlets 9 months after initiation. Histological analyses demonstrated that late plant regeneration from established callus and suspension cultures occured through organogenesis, although some embryogenesis events may have taken place during initiation of these cultures.
